1. Field of the Invention
This invention relates to imaging in optical code reading devices. Aspects of the invention are particularly useful in solid state, area image sensor based, handheld code readers that are positioned at variable orientations and distances with respect to a target code.
2. Description of the Related Art
Optical code readers are used in fixed or portable installations in many diverse environments such as in stores for checkout services, in manufacturing locations for workflow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target barcode from a printed listing of many barcodes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a handheld sensor that is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional barcode symbols. The barcode is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one-dimensional barcode is the UPC/EAN code used to identify, for example, product inventory. An example of a two-dimensional or stacked barcode is the PDF417 barcode. Another conventional optical code is known as “MaxiCode.” It consists of a central finder pattern or bull's eye center and a grid of hexagons surrounding the central finder.
It is noted that the aspects of the inventions disclosed herein are applicable to optical code readers, in general, without regard to the particular type of optical codes which they are adapted to read. The invention described may also be applicable to some associated image recognition or analysis.
Most conventional scanning systems generate one or more beams of laser light, which reflects off a barcode symbol, and back to the scanning system. The system obtains a continuous analog waveform corresponding to the light reflected by the code along one or more scan lines of the system. The system then decodes the waveform to extract information from the barcode. A system of this general type is disclosed, for example, in U.S. Pat. No. 4,251,798, assigned to Symbol Technologies, Inc. A beam scanning system for detecting and decoding one and two-dimensional barcodes is disclosed in U.S. Pat. No. 5,561,283 also assigned to Symbol Technologies, Inc.
Barcodes can also be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of cells or photo sensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a two-dimensional or area charge coupled device (CCD) and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view.
Such scanning systems are deployed in handheld units that may be manually pointed at the target. Often an individual scanner is a component of a much larger system including other scanners, computers, cabling, data terminals, etc. Such systems are frequently designed and constructed based on mechanical and optical specifications for the scanning engine, sometimes called “form factors.” One such form factor is the SE1200 form factor designed by Symbol Technologies, Inc.
Optical codes can also be read by employing optical code readers having an imaging engine. An imaging engine includes an image sensor having a two-dimensional array of cells or photo sensors, such as an area charge coupled device (CCD), which correspond to image elements or pixels in a field of view of the imaging engine. The imaging engine further includes a lens assembly for focusing light incident on the image sensor and associated circuitry coupled to the image sensor.
The associated circuitry produces electronic signals corresponding to a two-dimensional array of pixel information for the field of view. The electrical signals are processed for extracting information indicative of the focus quality of an image corresponding to the field of view.
An object of the present invention is to provide a more versatile optical code reader than prior art optical code readers.
It is an object of the present invention to provide a simple and inexpensively fabricated optical system for an optical code imaging engine having structure for providing more than one depth of field.
It is another object of the present invention to provide an imaging engine having an image modification assembly for changing the depth of field of an image in accordance with a determined focus quality for adjusting the image quality of an imaging optical code reader.
It is another object of the present invention to provide an imaging engine which can be substituted for conventional laser line scanning engines, in currently designed and currently deployed optical code reader systems and which includes structure for providing more than one depth of field to increase the reliability, versatility, and target working range of such systems.
It is another object of the present invention to provide an imaging optical code reader having an image modification assembly for providing more than one depth of field.
It is another object of the present invention to provide an imaging optical code reader having an image modification assembly for providing a plurality of selectable depths of field appropriate to the signal processing and decoding capabilities of the reader.